Can rotation solve the Hubble Puzzle?
academic.oup.com
academic.oup.com
There's really no way to know if there was something in existence before the big bang however. We just lack evidence of such a thing.
It is true that in GR you can't speak of "before" the big bang, but the big bang itself is a feature within time. It happens at the first moments of time and everywhere in space. And if you replace the initial singularity with a dense quantum foam and thus are able to extend time into the past in some quantum sense, the big bang doesn't go away.
If you have two stars orbiting each other, they orbit a centre of gravity and they will probably both be rotating in the same direction as their orbits.
Is that a meaningful centre for anything else though?
To say that the universe rotates usually implies that it rotates with respect to something external. If we limit ourselves to the visible universe, this would mean that mass outside our light cones can actually influence us, by means of building the frame of reference that allows us to say that the universe rotates!
It would imply that there exist privileged reference points within the universe, and that would be a major change to physics. I can't predict all of the consequences of that, and they might include some kind of external frame of reference. But that doesn't necessarily follow.
Which would undercut practically all of modern physics. Really fundamental conservation laws like momentum and energy rely on the universe being equal in all directions. If it has a central axis, that does not hold.
So if that holds, it's potentially a major pointer to the very origins of the universe itself. But it's also one of those extraordinary claims that require extraordinary proof. I strongly doubt that this will stand up to scrutiny -- though I'll certainly be pleased if it turns out be true, because that will be a major advance in our understanding.
And also from the abstract:
> Curiously, this is close to the maximal rotation, avoiding closed time-like loops with a tangential velocity less than the speed of light at the horizon.
That's weird considering that in lambda CDM the universe's accelerating expansion implies that stuff falls out of our observable universe, which implies that there is more stuff beyond the edge of the observable universe, and anyways there is no center of the universe and we are only at the center of our observable universe, which also further implies that there is stuff beyond the observable universe. Are they saying that our observable universe has a rate of rotation such that the tangential velocity at the edge is about the speed of light? What about the stuff beyond the edge? And as u/BigParm wonders, doesn't having the whole universe rotate imply a center? Surely we can't be at that center. But maybe there can be an illusion that we are at the center of rotation.
"Obviously you are not convinced that this is the end of the universe. if you will place a quarter in the slot below, the peep-hole will open, and you can see for yourself."
And the captain was right. I paid my quarter and looked through the peep-hole. But it was nothing.
--From "Ado about Nothing, by Robert K. Ottum
It's much like the expansion of the universe, which is separate from the ordinary momentum of the objects within the universe. But the objects within the universe do move apart along with it.
These things really challenge my physics intuition!
(I was/am skeptical just because it's a single-author study with pretty spectacular results, and have been keeping an eye out for any followups, but must have missed them)
It's unfortunately rare for this kind of straightforward falsification to make it into publications aimed at the general reader. "A lie is halfway round the world before the truth has got its boots on," as they say.
I was hoping for something a bit more authoritative than a reddit comment being copy/pasted to HN (e.g. an actual retraction, or a paper directly disputing the findings), but I'm guessing most of the community just ignored the paper due to the history of the author.
No, it doesn't.
I was hoping to read something that addressed this specific paper. All of those links are papers published before Lior Shamir's paper was published.
The comment I originally replied to said "people pointed out he cherry-picked results". I thought "people" might be "scientists" and they might have pointed it out in a subsequent paper or something.
Thanks though.
The cherry picking is clear from the difference in results not their timing.
I meant the rebuttal usually doesn't get published with the same high profile as the original story.
There is no "space itself" because then you're assuming it is relative, like the speed of light. Basically you're trying to rediscover the aether.
That was the question: light moves at speed C, but relative to what?
Oops, it turns out we used the name too soon.
When people say "universe" these days they mean the "visible universe" (or maybe the visible universe plus the stuff we're sure is there, but that falls outside our light cone now) - and not the original definition of the word anymore.
(Not that we have "found" anything else yet.)
They are aptly named.
Rotation is absolute. Unlike linear motion, you can tell if you're sitting in a rotating frame of reference or not. Experiments such as the Coriolis force, and Foucault's pendulum, are demonstrations of this principle.
In fact, a historical oddity is that when this idea was nailed down by both theory and experiment, the Catholic Church dropped its ban on heliocentrism. (Not that it mattered, the horse had already left the barn).
There are stringent constraints on anisotropy from the cosmic microwave background.
In particular, one can use the Doppler effect to check whether the CMB dipole is compatible with our velocity with respect to the CMB frame.
However, a 2016 study compared isotropic and anisotropic cosmological models against WMAP and Planck data and found no evidence for anisotropy.
My money’s on non-infinite, just because I’m not sure infinity is a well-defined concept outside of mathematics. We’ve certainly never observed any other infinite phenomena.
Infinity extends both upwards and downwards in scale.
We don’t know if that is the case. That is only one possibility.
But it seems very clear that whatever happens at the Planck distance or lower isn’t simple smooth space as we model it for larger scales.
The “relativity” aspect will almost certainly still apply in some way, and still form an emergent basis for the special relativity effects you point out.
All of general relativity has to be emergent from the to-be-discovered laws of the underlying small scale structure of space.
(I.e. general relativity isn’t wrong, it is just not complete. Similar relationship as with Newton’s Law of Gravity, which was also correct, but breaks down beyond the conditions it covers well, because it was not complete.)
The smallest scale is also where we expect more “light” shed on the initial conditions of the universe and potentially the insides of black holes. Two other conditions where general relativity already breaks down.
It doesn’t that any particular phenomena we understand today will break down. Just we will be able to see richer behavior, that has been there all along, than our models cover today. And so be able to understand more conditions than we do today. And perhaps new capabilities to engineer things than we have today.
Obviously quantum field theory, as it exists today, breaks down at the Planck distance too, since it can’t tell us what is happening at smaller distances either.
This isn’t the least bit controversial or surprising. It just means that even with both theories, we can’t explain everything yet.
When we do have an accurate theory of the fine structure of space and time, it will also be a theory of the fine structure of fields. Since space-time is integral to both theories.
It may even be the long sought after unification.
But for distances much larger than the Plank distance, the fine structure theory will still simplify into the GR and QFT we have today.
Just as GR under many conditions we encounter every day, further simplifies to Newton’s Law of Gravity.
For examples of the "good" kind, Newton's laws of motion are indeed just an approximation of special relativity. The Schrodinger equation is just an approximation of QFT.
In contrast, GR came in and showed that Newton's law of universal attraction is completely wrong, at the fundamental level. Sure, it predicts certain phenomena correctly, but so did the epicycles that it replaced. Similarly, QM/QFT showed that Newton's laws of motion are also completely wrong, that objects (or at least particles) don't even move according to some laws of motion, they are only described by a probability wave that moves according to some laws, and between two interactions they have no definite state and are not even localized.
And of course, GR and QFT disagree on these parts - GR generally agrees with Newton's laws of motion (with the SR corrections), and QFT generally agrees with Newtoninan gravity. But you can't use GR's gravity with QFT's laws of motion, so we know one or both are broken. A new theory is very likely to also "overrule" one or both of them and show that they are not just an approximation, but completely wrong, working only "by accident" on the scenarios where they have been tested. Especially if the new theory requires there to exist fixed space distances that all relativistic observers agree on.
People (some people) think that the universe really is that way, at the Planck distance. Actual experimental confirmation is somewhat lacking at this time...
I've also heard that there's nothing special about planck length other than it being universal constant that we and any conceivable aliens would agree on as a standard of measure. So, idk.
This is just according to our current theories, and you don't need any speculative ideas about granularity of space. Mathematically, there's no problem in considering arbitrarily small length scales, because current theories are based on continuous space and time dimensions, but since we can't give physical meaning to small length scales, that's a clue that a more fundamental theory will somehow not be based on continuous space and time
To my understanding there's nothing special about it except once you get to quantum field theory, and specifically spin-2 particles, which are the ones that hypothetically carry gravity (i.e. gravitons). (They're hypothetically gravitons because mathematically they result in conservation of the "stress-energy tensor", which is the same thing that Einstein's field equations give. And this isn't coincidence; it's because both are second-order field theories preserving Lorentz transforms aka special relativity). But notably if you only get through non-relativistic quantum mechanics, there's nothing special that happens at Planck length.
Planck length becomes special in QFT because at Planck length, the feedback (my force on you affects your force on me affects my force on you etc) of the quantum field mathematically explodes in something called "UV divergence". Notably, this also happens for other force carriers, not just gravitons, but a mathematical trick called Renormalization fixes that. Renormalization is based on shady techniques like assuming the sum of all whole numbers is -1/12. (IIUC this is a fairly straightforward pure mathematical result from complex analysis, required to ensure consistency of Fourier transforms for infinite sequences, known as analytic continuation / Riemann zeta function. Of course it makes no sense that nature should behave that way, but one day some physicists thought "let's try this weird math" and it matched experiments). However that technique only works for lower-spin fields (E&M, weak, strong) because the feedback is linear, hence sum(1+2+3+...). But in spin-2 fields the feedback is (quadratic? exponential?), and the same trick still gives an infinite result.
Ultimately one could say this is the only thing standing in the way of a complete theory of quantum gravity. If we could get the math for gravitons not to blow up at tiny scales, we'd be done (experimental verification notwithstanding). String theory is one attempt: "Let's say there are no point particles, only strings, and this problem goes away". Other approaches exist too. But ultimately right now, there's no way to say for sure whether sub-Planck exists, doesn't exist, exists in some ways but not in others, or whether all of physics is wrong and we have to start over.
A quick addendum: Planck energy is approximately the chemical energy in a tank of gas. Planck mass is about that of an amoeba (so an antimatter bomb made out of an amoeba would explode like a tank of gas (Hiroshima was 0.6 grams of mass), a photon with that energy would have a Planck-length wavelength, and an amoeba-mass black hole is Planck-length). Given there's nothing overly special about Planck energy or mass, my money is on there being nothing special about Planck length either.
Hopefully at least some of the above is correct.
https://www.youtube.com/watch?v=-OxVsVUesSc
About the Planck length, while the length itself might not be physically significant, black holes are definitely physically significant, and according to the current thinking there will be some smallest length that can be probed before what you're looking at becomes a black hole. I guess I was lazily assuming that would be around the Planck length. I would have to look into it more to come up with a calculation for that
Anyway, we don't actually know that, since we do not have a time machine. The theory that the universe used to be much smaller is something we infer based on the snapshot we see today, just like we infer rotation based on the snapshot we see today. Either one could yet be proven wrong.
If you take the number like and apply f(x) = 2x, it was infinite before and after.
The number line is not finite, even though every value on it is. The universe may be like the number line.
> and given that it started out being very small in a big bang, it would imply the former
The universe started out denser, which is not quite the same as "small" when talking about infinities. The currently visible universe gets both things at the same time, but only because the visible bit is finite.
Apply f(x) = x * 1e-60 to the number line, and things which were previously spaced out every integer, are now much more densely packed, but the number line as a whole is still the same size — infinite.
f(x) = 1/(1-x)
So if x is finite, f(x) can still be infinite.
Because they're opposites, they depend on each other's existence. Like hot cannot exist without cold, or light doesn't have any meaning if there is no darkness.
The observation could also be due to an area of relatively high density inside an area of relatively no density.
Gödel wait what? I thought of him as “only” the logician who killed Hiblert’s dreams and caused people to question the very foundations of mathematics.
Dude then took up physics as a hobby and trolled Einstein by discovering closed time-like curves?
Also, from Wikipedia: “At age 18 [so around 1924], Gödel joined his brother at the University of Vienna. He had already mastered university-level mathematics. Although initially intending to study theoretical physics [we can assume that’d include an interest in relativity at that time], he also attended courses on mathematics and philosophy.”
Is this a reasonable conclusion?